Helicopter deployed underwater electronic equipment such as mine sweepers as well as other sensors and devices such as unmanned undersea vehicles, torpedoes, and submarines are subject to corrosion. In the case of helicopter deployed equipment, the motion of the rotor blades through the air results in the accumulation of electrostatic charges on the helicopter (sometimes 100 kV or more) which would be discharged from the helicopter to the water, through the tether between the helicopter and the towed equipment damaging the internal electronic subsystems of the towed equipment. Typically, to prevent this electrostatic discharge damage, a ground wire is run from the helicopter to a terminal connected to the hull of the towed equipment via a fastener. Surface corrosion protection treatments cannot be used at the threaded interface between the fastener and the hull of the towed equipment due to the need for a good electrical connection. Thus, the threaded hole in the towed equipment hull in which the fastener is installed is subject to general corrosion, crevice corrosion, and galvanic corrosion.
The result is that after deployment and retrieval of the towed equipment, personnel must inspect and if necessary clean and refurbish the connection between the ground wire terminal, the fastener and the hull of the towed equipment. Typically, the fastener and terminal are removed from the hull of the towed equipment breaking the ground connection. In any case, the inspection, cleaning, and refurbishment effort can be costly and time consuming.
There are also other scenarios where a fastener is threaded into the hull of an underwater deployed sensor or device and subject to corrosion. One example is cathodic protection terminals wherein a zinc slug is connected to a fastener threaded into the hull of a torpedo or submarine. Again, the threaded interface between the hull of the torpedo or submarine and the fastener is subject to corrosion.